1. Field of the Invention
The present invention relates to an ink set having excellent color reproduction, and an ink jet recording method.
2. Background Art
Ink jet recording is a printing method wherein droplets of an ink composition are ejected and deposited on recording media, such as paper, to perform printing. The feature of the ink jet recording method is that images having high quality with high resolution can be printed at a high speed by means of a relatively inexpensive apparatus.
In recent years, a plurality of chromatic color ink compositions are used for ink jet recording to form a color image. In general, a color image is formed by using three color ink compositions, i.e., a yellow ink composition, a magenta ink composition, and a cyan ink composition, or four color ink compositions, i.e., the above three color ink compositions and additionally a black ink composition, or six color ink compositions, i.e., the above four color ink compositions and additionally a (light) cyan ink composition having a lower color density and a (light) magenta ink composition having a lower color density.
When ink dots formed by the plurality of color inks are allowed to be present in a mixed state, a variety of colors can be printed.
A color image having a low-lightness (dark) can be printed by forming, in a mixed state, ink dots of three colors of cyan color, magenta color, and yellow color. For example, ink dots of cyan color, ink dots of magenta color, and ink dots of yellow color are formed in substantially equal amounts so as to be mixed with one another, the image is visually perceived as a black image due to subtraction color mixing. The black expressed in this way is called “composite black.”
In general, for recording media, from the viewpoint of avoiding a deterioration in image quality caused by bleeding of ink or the like, a predetermined target for the total amount of ink dots formed per unit area is provided. The target value for the total amount of ink dots is generally called “ink duty limit value.”
When composite black is used for printing a low-lightness (dark) color image, three types of ink dots should be formed. In this case, disadvantageously, the total amount of ink dots sometimes exceeds the ink duty limit value, often leading to deteriorated image quality. On the other hand, when the ink duty limit value is much larger than the amount of ink deposited, a phenomenon that blank spaces are left in the image, that is, a phenomenon called “white spots,” sometimes disadvantageously occurs. To avoid this unfavorable phenomenon, a method is adopted in which a black ink is provided in a color printer and ink dots of the black ink per se are used instead of the composite black.
In general, however, dots formed by the black ink are so conspicuous that, for some image, due to the conspicuous dots, granular feeling sometimes occurs in the formed image.
Further, in ink compositions, good fixation of colorants onto recording media is required. For example, the ink composition is required to yield an image having rubbing/scratch resistance on such a level that, when the image deposited on a recording medium is rubbed with a finger, a printing implement (for example, a line marker) or the like, the image does not become dirty. In order to meet this requirement, Japanese Patent Laid-Open No. 81366/2001 proposes an ink comprising a colorant and resin particles, and Japanese Patent Laid-Open No. 80761/2002 proposes an ink composition for ink jet recording, comprising an aqueous medium of pigment and resin particles.
However, there is still a demand for an ink composition and an ink set having various excellent properties, especially an ink composition and an ink set having excellent image reproduction, color reproduction, and fixation, and an ink jet recording method using the same.